Last Month's Most Accessed Feature: Turbulence under the sun: Determining exposure to sunscreen ingredients

Monthly Highlight

Published: Mar 1, 2018

Categories: Sample Preparation

Expsoure to sun and sunscreen

We’re constantly being warned about the potential dangers of prolonged exposure to the sun’s rays on hot days, and how we should always make sure to cover ourselves in sunscreen. But what about the potential dangers of all this exposure to sunscreen? While no one is suggesting that going out into the full glare of the summer sun without sunscreen is a good idea, little is known about the long-term health effects of some of the ingredients in sunscreen or even about our level of exposure to them.

Obviously, our main exposure to these ingredients is through applying sunscreen directly to our skin, but at some point that sunscreen is then washed off in the bath, shower, swimming pool or sea. In this way, sunscreen makes its way into the wider environment, enhancing our exposure and also causing wildlife, especially marine wildlife, to become exposed to its ingredients.

Metabolites in urine

Commonly used in sunscreens since the early 2000s, octocrylene absorbs ultraviolet (UV) light, specifically the wavelengths known as UVB, preventing them from reaching and damaging the skin. As an added benefit, it also helps to stabilize another ingredient called avobenzone, which absorbs UVA wavelengths. The German Federal Ministry for the Environment has identified octocrylene as a substance for which exposure levels need to be determined, hence the interest in developing a monitoring method.

To develop such a method, Bury and his team first looked for metabolites of octocrylene that could be detected in urine, as this is easy to obtain. They identified three plausible candidates and then investigated how they fragmented in mass spectrometry (MS), in order to identify characteristic patterns of fragmentation that could be used to identify them.

Before the metabolites can be identified by MS, however, they need to be separated from the many other components in urine, for which Bury and his team employed a combination of turbulent flow chromatography (TFC) and liquid chromatography (LC). TFC is a sample preparation method commonly used for separating small molecule drugs from the other components of urine, particularly large biomolecules, prior to analysis by LC-MS.

Large particles and high flow

One of the great advantages of TFC over other sample preparation methods, such as solid-phase extraction, is that it can be combined directly with LC, rather than performed as a separate step, allowing analytes to flow seamlessly from TFC to LC. It uses much larger particles as the stationary phase than conventional LC and injects the sample at a much higher flow rate. Between them, the large particles and high flow rate generate turbulence within the column.

This turbulence has a much greater effect on the small molecules than the large biomolecules, driving the small molecules into pores in the particles, where they can bind with functional groups. In contrast, the larger biomolecules, which are too big to fit into the pores, pass straight through the column. The small molecules can then be eluted for analysis by LC-MS.

Using their combination of TFC, LC and MS, Bury and his team found they could detect the three octocrylene metabolites in urine at sub-microgram per liter concentrations. As a test monitoring study, they then used the method to analyze urine samples from 35 people, detecting at least one of the metabolites in 32 of the samples.

Confirming the accuracy of the method, they detected the highest concentrations of all three metabolites in three people who reported applying sunscreen within five days of providing the urine samples. The other 32 people hadn’t applied sunscreen within the preceding five days. Seeing as the samples were collected in Germany during April, the three people who had applied sunscreen were perhaps erring on the side of caution.

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